I can't find how to edit code inside the program?

Hello I would like to know how can I edit or if I can edit the files/code from .jar file that I Imported inside the program?
I want to edit messages from .jar file if it's okey... :D

Review the program's documented editor workflow and the imported .jar workflow to determine whether users can edit messages or code in place. Document the relevant entry point and steps if supported; otherwise make the limitation explicit and point users to the supported workflow.

Written by the indexing model from the issue text.